Application study of magnetic reconnection for high temperature spherical tokamak formation*

Here we present the latest report of our application/exploration of high field reconnection heating in ST40 and TS-6 merging spherical tokamak formation experiments. MAST-like high performance scenario has successfully been reproduced in ST40, and TS-6 explores further investigation of heating/transport process using the full-2D Dopploer tomography diagnostics. Based on the experimental scaling ΔT_i ∝ B_rec² by outflow heating mechanism and the saturation of guide field dependence on reconnection heating in high guide field regime B_t (guide field)/B_rec (reconnecting field) > 3, both projects selected high B_rec for more heating and high B_t /B_rec to suppress perpendicular heat conduction with the weight of κⁱ_∥/κⁱ_⊥ ~ 2(ω_ciτ_ii)² >>1 as a standard plasma scenario. The sustainment of the high temperature plasma in τ_duration >> τ_merging has successfully been demonstrated in both projects and it was found that the characteristic double-peak T_i structure is sustained after the end of outflow acceleration/heating for longer time scale than the merging process. The propagation process of high T_i area is affected by guide field polarity and it was found that the positive potential side of guide field reconnection has higher T_i through parallel acceleration and globally gyrating heat transport.